Electronic stress-strain recorder



April 22, 1952 B. SCHLACHMAN ETAL 2,593,493

ELECTRONIC STRESS-STRAIN RECORDER 3 Sheets-Sheet 1 Filed June 10, 1949mm mmECbmm mymjmsi il. v

muECbum INVENTQRS BENJAMIN SCHLACHMAN WILLIAM s. BROWER, JR. (926WATTORNEY A ril 22, 1952 a. SCHLACHMAN ET AL 2,593,493 I ELECTRONICSTRESS-STRAIN RECQRDER 3 Sheets-Sheet 2 Filed June 10. 1949 iNVENTORSBENJAMIN SCHLAGHMAN WILLIAM S. BROWER, JR. BY (96W ATTORNEY April 1952B. SCHLACHMAN ETAL 2,593,493

ELECTRONIC STRESS-STRAIN RECORDER 3 Sheets-Sheet 3 Filed June 10, 1949mvemoRs BENJAMIN SCHLAGHMAN WILLIAM S. BROWER, JR.

BY Q (9/2;

ATTORNEY Patented Apr. 22, 1952 2,593,493 ELECTRONIC STRESS-STRAINRECORDER Benjamin Schlachman,

William S. Brower, J

Baltimore, Md, and r., Arlington, Va.

Application June 10, 1949, Serial No. 98,342

2 Claims. (01. 177-351) (Granted under the act of amended April 30,1928;

The present invention relates primarily to stress-strain recorders andmore particularly to an electronically controlled compensating devicefor recording the deflections of an element undergoing a stress-straintest, although applicable to the recordation of mechanical movementgenerally.

The present recording stress-strain testers are limited to testingsimple specimens for straight compression or tension with smalldeflections. In the present development of industrial machinery andappliances, however, it is necessary to make more elaborate tests thanare permitted by these recording machines. Heretofore, when moreelaborate testing was required it has been necessary to measure thedeflection of parts under test with dial indicators, requiring theattention of many operators during the test and resulting in frequenterrors in making the readings and plotting performance curves therefrom.

It is one object of the present invention to provide for automaticallyrecording the extensions and compressions of specimens of the morecomplex type as Well as the simpler, and to afford a means whereby themechanical deflections are converted into electric impulses which aretransmitted through a suitable circuit for effectuating an automaticrecordation of the deflections upon a suitable recording device. To thisend there is provided a means whereby the deflection of a dial typestress-strain indicator is automatically and directly converted into anelectric signal which by means of an electronic circuit controls amechanical system operating to compensate the electric signal andthereby to record the deflection of the tested elements.

Another object is to provide an electronic compensating control circuitwhich will efiectuate the above described object by actuating a suitablemechanical linkage in response to said signal current, said linkageoperating upon the signal producing means to reduce the signal currentto zero and thereby correspondingly operating a recording device.

A dial type stress-strain indicator is used as the initial mechanicalimpulse receiving element, it responding to the deflection of theelement being tested. This mechanical impulse is converted into anelectric signal by means of a suitable circuit composed of a pair ofsynchronously connected generators in the form of a control transformersystem. A suitable current is applied to the rotor of the transmittinggenerator which is mechanically connected to the pointer shaft of a dialindicator type stress-strain tester. The

March 3, 1883, as 370 O. G. 757) stator of this transmitter issynchronously connected to the stator of the receiving generator suchthat movement of the transmitting rotor out of synchronous relation withthe receiving rotor as caused by the stress-strain indicator causes avoltage to be induced across the receiving rotor, but when the receivingrotor is brought into the corresponding position then existent in thetransmitting rotor the voltage induced in the receiving rotor is reducedto zero. Thus, movement of the transmitting rotor induces a voltageacross the receiving rotor thereby converting the mechanical movement ofthe element being tested into an electric signal.

The current thus generated is then amplified and applied to the grids ofa suitable control vacuum tube in order to control the flow of currentto a relay, the control tube being in the relay energizing circuit. Therelay in turn controls the operation of a pair of solenoids, being inseries in their energizing circuit. Thus, the operation of thesesolenoids is controlled by the signal current, all to be more fullydescribed in detail below. The solenoids operate a clutch in a gearingsystem driven by a suitable servo motor or the like. This gearing systemhas a two-fold function: one being to rotate the drum of a recorder, theother being to turn the rotor of the receiving generator of thesynchronous circuit above described to bring it into synchronism withthe transmitting rotor and thus reduce the voltage induced across thereceiving rotor to zero.

The operation of this system is briefly a follows: A dial indicator typestress-strain tester or similar device is applied to an element to; betested. The pointer is mechanically connected to a synchronous controltransformer system, as by an axially extending shaft and suitablecoupling, so that movement thereof during the test is converted into anelectric impulse by said synchronous system. The signal voltage producedthereby is used to control the solenoids which in turn operate theclutch in the gearing system. Thus, so long as the receiving rotor isout of synchronism with the transmitting rotor the gearing system,through the solenoid operated clutch, moves the receiving rotor to bringit into synchronism with the transmitting rotor and simultaneously movesthe recording drum in accordance with the movement imparted to thereceiving rotor. When a synchronous relation between the two generatorsis reached, the solenoid operated clutch disengages the servo motor drumfrom the gear train, and the receiving rotor and recording drum remainstationary until further deflection of the element being tested causes anonsynchronous relation between the two generators. It is thereforeapparent that this device operates to continually compensate for thesignal current as actuated thereby and simultaneously operates to recordthe amount of compensation required as a measure of the deflection ofthe piece being tested.

The pen arm of the recorder is responsive to the force applied to thetested element during the testing process and moves lengthwise along therecording drum proportionally to said force. Thus a record of thedeflections of the element being tested is automatically plotted againstthe force applied thereto.

The present invention, described broadly above is hereinbelow describedin detail in conjunction with the accompanying drawings, wherein likenumerals refer to the same or corresponding parts in the difierentdrawings.

Fig. 1 is a partially schematic block representation of the circuitemployed by the present invention;

Fig. 2 is a detailed wiring diagram of the circuit of the presentinvention; and

Fig. 3 is a schematic representation of the gear train and drumrecorder.

Referring to Fig. 1, the signal generating circuit comprises a pair ofsynchronously connected generators forming a control transformer systemI having a transmitting generator II with a suitable voltage, such as 26volts at 400 cycles, applied to its rotor, and a receiving generator I2.A voltage is induced across the rotor of generator I2 when the rotor ofgenerator II is caused to move out of synchronism with the rotor ofgenerator I2, which movement is caused by the rotation of the pointer ofa dial indicator type stress-strain tester applied to the transmittingrotor. The signal voltage thus induced across the rotor of receivinggenerator I2 is amplified in amplifying system 20.

The control circuit of relay 30 receives its operating current fromtransformer but is controlled by the amplified signal current by meansof control vacuum tube I00. The relay functions as a control of thesolenoids, either compression solenoid or tension solenoid 55, dependingupon the position of the manually operated switch I30. The solenoidsoperate to cause clutch 10 to engage either gear II or I2 when relay 30is energized, depending upon the position of switch I30, or to bedisengaged from both gears when said relay is not activated.

As mentioned above, the relay 30 is controlled by the amplified signalcurrent by means of vacuum tube I00, preferably type 6N7, functioningboth as a rectifier and an electronic switch. Leads 4| and 42 fromtransformer 40 are connected to anode plates IOI and I02 of tube I00applying preferably about 190 volts A. C. thereto, and the voltage soimpressed on each of the plates being always 180 out of phase with thatimpressed on the other plate. The current leaving amplifier 20 is passedthrough a 1:5 transformer 80 and the voltage thereof is applied to thecontrol grids I03 and I04 in tube I00. Therefore, current will flow fromeither filament I05 of tube I00 to plate IOI or to plate I02 thenthrough a portion of the secondary 43 of transformer 40, and throughlead 44 to activate relay 30 if grids I03 and I04 have a proper voltageapplied thereof. Otherwise, relay 30 is deactivated.

' Thus, grids I03 and I04 carry the voltage induced in the rotor ofreceiving generator I2 as amplified. When the rotor of transmittinggenerator II is turned a voltage is induced across the rotor ofreceiving generator I2. The current thus generated is amplified inamplifier 20, the voltage thereof is stepped up in transformer 80, andthis voltage is applied to grids I03 and I04 to control the passage ofcurrent from the cathode to the plates of tube I00 and hence results inthe activation of relay 30. In operation, with zero A. C. voltageapplied to the grids I03 and I04 they are biased by variable resistanceI01 to place relay 30 on the verge of activation. Then when either gridI03 or I04 becomes more positive and its respective plate IOI or I02 ispositive with respect to the cathode I05, an increased current can flowto the relay causing it to close the circuit to the solenoids. The gridsattain this increase in positive potential with respect to the cathodeby means of the amplified A. C. signal current impressed thereon.

Fig. 2 is a detailed view of the entire electrical circuit which showsthe synchronously connected generators II and I2 and their wiringconnections, the transmitting stator I3 and rotor I4, and the receivingstator and rotor I5 and I6, respectively. The synchronously coupledgenerators II and I2 may be of any suitable design such asEclipse-Pioneer Autosyn type AY101D. Leads I20 and I2I conduct thecurrent induced on rotor IE to the three way gang switch I30, shown inoff position and to be discussed fully below, and the voltage thereof isapplied to amplifier 20 by means of lead I22, said amplifier beingprimarily a vacuum tube of type 6SJ7. Lead I22 thus impresses thevoltage induced on rotor I6 on grid 2I of tube 22 effectuatin anamplified output in accordance with the current induced on rotor I6. Thevoltage of this amplified output is stepped up 521 in transformer 80.This transformer, acting as a high impedance load, and the 0.01microfarad condenser 8|, cooperating therewith to filter out the highfrequency currents, produce a pure sine wave of 400 cycles, the voltageof which is applied to grids I03 and I04 of tube I00 through leads 82and 83. As explained above, when the voltage of both grid I03 and plateIOI or grid I04 and plate I02 carry a proper potential with respect tothe cathode, current flows through lead 44 to energize an armature coil32 of the relay 30 and thus cause an armature 33, which is normallyengaged with an upper relay contact 34, to be moved into engagement witha lower contact 35, whereby either solenoid 50 or 55 is activated,depending on the position of switch I30, upon a suificient fiow ofcurrent to activate the relay.

The three bank selector switch I30 mentioned above has a triple throw.The center throw is the oii position as shown in Fig. 2. Either the leftor right throw will effectuate closing of the circuit connecting rotorI6 with grid 2|. However, the two on throws are for the purpose ofselectively choosing either solenoid 50 or 55 for actuation of theclutch I0, all of which will be more fully discussed hereafter inconnection with the description of the mechanical gear train and itsassociated parts for rotating the drum recorder and the rotor I6 ofreceiving generator I2.

The operating current of the amplifier is supplied thereto by means ofrectifier employ-' ing a rectifying vacuum tube type 6X5. The volt 60cycle current source for operating the solenoids 50 and 55 is rectifiedby bridge recart-sages tifier 95. Other usual parts of the variousconventional circuits are shown in Fig. 2 by their conventional symbolswith their values indicated when of significance.

The mechanical gear train and its associated parts, mentioned above andshown schematically in Fig. 3, comprises a suitable power unit,preferably a servomotor or the like I40, connected to bevel gear I45 forrotation thereof, which in turn drives bevel gears II and 12 in oppositedirections. Clutch I is keyed to shaft I49 and is slideable therealongto selectively engage, either gear II or I2 depending on the directionof rotation desired or stands free of either gear when no rotation isdesired. Rod I49 connects clutch I0 with worm gear I50 for rotation ofshaft II. Shaft I5I operates at one end to drive rotor I6 of thesynchronous receiving generator I2, and at the other end is suitablycoupled to shaft I52 by means of flexible coupling I53 to drive therecording drum I60 through a variable gear box IIiI.

Selective clutch I0 operates between three positions: in engagement withgear II, in engagement with gear 12, or in neutral position disengagedfrom either gear. The various positions of the clutch are effectuated bymeans of solenoids 50 and 55, operated by current supplied from bridgerectifier 95 and actuated by relay 30.

During the compression phase of the stressstrain test on an apparatus,while the load thereon is being increased, selector switch I30 is thrownto the right to stop I3I thereby closing the circuit between therectifier 05 and the compression solenoid 50 when relay 30 is activated;during the tension stage of the test, while the load is being reduced,the switch is thrown to the left, to stop I32, thereby closing thecircuit to the tension solenoid 55 when relay 30 is activated. When thiscircuit is closed to the compression solenoid 50, clutch I0 engages withgear II to rotate the rotor of receiving generator I2 in one direction;and when this circuit is closed to the tension solenoid 55 the clutchengages with gear I2 to rotate said rotor in the opposite direction.Likewise, as will be readily observed from Fig. 3, with. the activationof one solenoid the recording drum I60 is rotated in one direction,while activation of the other solenoid causes said drum to be rotated inthe opposite direction.

In the operation of this apparatus, a conventional dial test indicatordrive may be connected to the rotor of the transmitting generator II,and may be properly positioned upon the device to be tested in the usualmanner. With the A. C. voltage on grids I03 and I04 of control tube I00at zero, these grids are biased with D. 0. current from rectifier 90through rheostat I01 so that the current flowing through relay coil 32as indicated by ammeter 3| places the relay on the verge of activation.The requisite biasing potential is about 4 volts when the suggestedequipment and current values are used. The rotors I4 and I6 of the twosynchronous generators are brought into synchronous position.

The first stage of the test is usually compression, increasing the loadon the device being tested, so selector switch I30 is thrown tocompression position I3I. As the pressure is increased, the dialindicator causes the rotor of transmitting generator II to rotate out ofsynchronous relation with rotor I6 of the receiving generator I2,thereby inducing a voltage on said rotor. This voltage is impressed onthe biased grids I03 and I04 as described above toactuate relay 30 andthereby close the compression solenoid circuit. The activation ofsolenoid 50 causes clutch 10 to engage gear II being rotated by force ofmotor I40. This engagement causes the clutch to rotate and thus throughrod I49, which passes free through gear 'II to engage clutch I0, andworm gear I50 to rotate both the drum I60 and the rotor I6 of receivinggenerator I2. This rotation is designed to be in a direction to followthe rotation of rotor I4 in transmitting generator II. Rotor I6 is thusagain brought into synchronous relation with rotor I4 and the voltageacross rotor I6 is thereby reduced to zero. Since there is now no signalvoltage being impressed on grids I03 and I04 of tube I00, the relaybecomes deenergized and the compression solenoid circuit is therebyopened. The clutch is thus forced back into neutral position by theaction of the solenoid and rotation of the recording drum and receivinggenerator rotor I5 ceases. However, as the compression increases, thetwo synchronized rotors I4 and I6 again fall out of synchronous relationand the above described operation is repeated. Thus the operation ofthis device provides an intermittent rotation of the rotor I6 and of therecording drum I60, representing the deflection of the device beingtested by rapidly following minute increments of rotation of rotor I4,while movement of the recording pen I62 along the length of the drumrepresents the amount of pressure applied, this latter movement beingeffected by any conventional means. Since in actual practice the periodsof activation and deactivation of the solenoids are short the curve thatis actually recorded on the drum is relatively smooth.

After the desired compression has been reached, the next step is torelease the pressure, called the tension phase of the test. At this timethe switch I30 is thrown to the left stop I32 to close the circuit tothe tension solenoid 55. The operation of the device during the tensionstage is identical to that for compression except that clutch I0 engagesgear I2 during activation of this solenoid to rotate rotor I6 and drumI60 in the opposite direction from that during the compression stage.The necessity for this change is readily apparent, for rotor I6 mustfollow rotor I4, and rotor I4 rotates in the opposite direction duringthis stage from the direction in the compression stage because of thechange of direction of rotation of the dial indicator. As the pressureis decreased, pen I62 moves in correspondence thereto. Thus a completecurve of the stress-strain characteristics of the device being tested isautomatically recorded on drum I60.

In the preferred embodiment of this invention, the entire apparatusexcept the transmitting generator II and its associated dial typestressstrain indicator are included within a unitary structure, theconnection necessary between these two units being merely a five strandcable including leads I1, I8, I9, 46 and 41. Because of the flexibleconnection between the two units and the compactness and lightness ofthe transmitting generator unit in the present invention, rather thanthe mechanical linkages and bulkiness of the conventional stress-strainrecording testers, many advantages are gained over the prior art: it maybe quickly installed on various elements to be tested; the deflection ofparts heretofore not easily accessible may be readily obtained; theneedle of the dial'indicator offers a convenient check of the recorderand its proper functioning; the same transmitting generator unit can beapplied to many variously shaped and formed elements; the dial indicatorunit can be mounted directly on the element being tested; and many otheradvantages will be readily apparent to those skilled in the art. V

The foregoing description presents a preferred embodiment of theinvention, but various modifications within the scope of this inventionas defined by the following claims will be apparent to those skilled inthe art.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor. 7

What is claimed is:

1. An electrical compensating device comprising a control transformercircuit for generating a voltage signal in response to mechanicalmovements, said circuit comprising synchronously connected transmittingand receiving generators, means for amplifying said signal, a controlvacuum tube comprising an anode plate element, a cathode, and a controlgrid, said amplified signal voltage being applied to said control grid,a relay, an operating circuit therefor, said tube being in series withsaid relay in its operating circuit through electrical connections withthe plate and cathode of said tube, said control grid, by control of thecurrent flowing between said cathode and said plate, controlling theoperation of said relay, means for biasing said grid to facilitatecontrol of said relay by said signal voltage, a pair of solenoids, acircuit for operating said solenoids, said circuit being controlled bysaid relay, a switching means independent of said relay having an offposition for preventing application of said signal voltage to said gridand having two on positions for applying said signal voltage to saidgrid and for selectively including one of said solenoids in saidsolenoid operating circuit, a mechanica1 linkage, a motor operating saidlinkage, a pair of clutches in said linkage individually operated bysaid solenoids,

and a recording drum, said linkage operating on said receiving generatorto reduce the signal voltage substantially to zero and simultaneouslyoperating said recording drum, the activation of one solenoid causingmovement of said linkage through said clutch in one direction,activation of the other solenoid causing movement thereof through saidclutch in the opposite direction, the deactivation of both solenoidsresulting in said clutch being positioned in a neutral position toeliminate movement of said linkage therethrough.

2. An electrical compensating device comprising a control transformerfor generating a voltage signal in response to mechanical movement ofeither of two directional senses, a relay, an electronic tube having aninput circuit responsive to said signal and an output circuitcontrolling said relay, a pair of solenoids, said solenoids beingcontrolled by said relay, a switching means independent of said relayhaving two on positions for applying said signal voltage to said tubeand for selecting one or the other of said solenoids to be controlled bysaid relay, and an independently driven mechanical linkage having aselective clutch means controlled by the solenoids, said linkageoperating on the control transformer as a follow-up means to reduce thesignal voltage substantially to zero through the switch selectedactivation of one solenoid or the other, one solenoid causing throughselective clutch means action follow-up in one directional sense, theother solenoid causing through selective clutch means action follow-upin the other directional sense.

BENJAMIN SCHLACHMAN. WILLIAM S. BROWER. JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,350,705 Clarke Aug. 24, 19202,415,680 Hoyt Feb. 11, 1947 2,439,094 Miles Apr. 6, 1948

